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Balsamic Mushroom and Caramelized Onion Pastry with Smoked Gruyere Cheese, Fresh Thyme and Rosemary

Caramelized onions, sautéed mushrooms & garlic, fresh rosemary & thyme, on a bed of puff pastry covered with melted Gruyère cheese. This recipe is absolutely delicious when eaten hot and fresh out of the oven and can be enjoyed as a lighter meal or served as an appetizer.

When I was a kid, I wouldn’t touch mushrooms. Mom would try to sneak them in my spaghetti or chop them up super fine in a casserole. I knew every one of her tricks, and I turned my nose up every time. I’m not really sure what changed other than maybe I liked mushrooms all along and was just trying to prove a point when I was younger…ha! I do know I LOVE them now, especially so when they’re paired with buttery, caramelized onions and hot, melted cheese. YUM!!!

Here’s the lowdown on caramelized onions. They make nearly every savory recipe a lot more “fancy schmancy,” but there’s nothing fancy about making them. Plus, you can make them ahead of time and refrigerate them, making food prep at recipe “go-time” that much quicker.

Pro tip: During the holidays, I like to make a big batch of caramelized onions to have on hand so I can just measure out what is needed for each recipe. Try this next time you have some serious cooking to do!

Another thing I love about this recipe is the fresh herbs. If you’ve learned anything about me so far, it’s that I use fresh herbs in nearly everything I make, and for this recipe, the rosemary and thyme takes this puff pastry treat to a whole “notha” level. Seriously, try it. It’s delicious!


  • 2 tablespoons butter

  • 1 small onion, diced

  • 1 tablespoon fresh thyme leaves

  • 1/2 tablespoon fresh rosemary, chopped

  • 1/2 teaspoon minced garlic

  • 14 oz sliced baby portobello mushrooms

  • 1 tablespoon balsamic vinegar

  • salt and pepper to taste

  • 6 ounces of shredded Gruyere cheese

  • 1 sheet puff pastry, thawed

  • 1 egg for brushing the edges


  • Preheat the oven to 375 degrees.

  • Heat butter in a nonstick skilled over medium heat. Once sizzling, add onions, rosemary and thyme to skillet and cook until they’re beginning to brown.

  • Add minced garlic to skillet with onions and herbs and cook for another minute or two; transfer to a plate or bowl to cool.

  • Then, add mushrooms to skillet and cook without stirring for 1-2 minutes. Add balsamic vinegar and cook until mushrooms have reduced their volume by half and liquid is evaporated. Let the mushrooms brown a little.

  • Transfer to dish with onions and herbs and let cool.

Assembly and baking:

  • Use a sharp knife to slightly score the puff pastry along all four sides of the dough (leaving about a 1-inch border), careful not to cut all the way through the dough. Transfer the pastry onto a baking sheet lined with parchment paper. Prick the dough (leaving 1-inch border untouched) with a fork.

  • Sprinkle cheese in an even layer over the dough.

  • Top with cooled mushrooms, onions and herbs.

  • Brush egg on the edges of the pastry. Prick the center of the dough with a fork a couple times more (not the edges). This step is important to not miss.

  • Bake for 25 minutes or until golden and flaky.

  • Enjoy every bite!


The Galloways

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